Vibratory conveying systems are commonly used in the food, and other industries, and where belt-type conveyors are undesirable, or where it is difficult to maintain the conveyors in a sanitary condition. Vibratory conveyors make use of a conveyor bed which includes an elongated tray which is made to vibrate predominately in a desired direction, and at an angle such that materials deposited on the bed will migrate or travel, at a selected speed, from an infeed end of the vibratory bed to a discharge end, thereof.
Excited frame vibratory conveying devices are known in the art. For example, U.S. Pat. No. 4,313,535, which is incorporated by reference herein, shows an exemplary excited frame conveying apparatus that has performed well in the past for transporting bulk product over relatively short distances. As a general matter, excited frame conveyors similar to that which is described, above, include a vibratory drive mounted on an elongated frame. The frame is supported or located on supporting surface, and the bed of the conveyor receives and moves product along the conveyor length. A resilient suspension in the form of leaf, or beam springs, project upwardly at spaced intervals along the frame and are inclined in the direction of the intake or infeed end of the conveyor. The elongated conveyor or product transporting bed is mounted on the upper ends of the respective beam or leaf springs. The conveyor bed is supported by the beam or leaf springs in a generally parallel relationship to the frame, and in a substantially overall, horizontal, orientation. Due to the resiliency of the respective beam or leaf springs, the product conveying bed is capable of reciprocally moving relative to the frame in response to a force applied to the bed by the vibratory drive mounted on the frame. During operation of the vibratory drive produces an oscillating or reciprocating vibratory force. This force may be generated by rotating eccentric weights mounted on the vibratory drive. As will be recognized, the vibratory drive is mounted on the frame and therefore imparts vibratory motion to the frame which is then transferred through the beam or leaf springs to the conveyor bed. As a result, the conveyor bed vibrates at substantially the same frequency as the drive and frame.
It should be understood that a conveyor bed that is displaced from its “at rest” position and then allowed to oscillate freely will oscillate at its natural or harmonic frequency. This frequency is dependent upon the combined spring constant, the number of springs supporting the conveyor bed, as well as the mass of the bed relative to the mass of the supporting frame.
As a general matter, and for conveyors of this design, less vibration and force is transferred to the underlying floor or other supporting structure by an excited frame conveyor because of the small vibrational amplitude of the frame as compared to the vibrational amplitude of the reciprocally moveable product conveying bed. The low level of vibrational force transferred to the surrounding structure is a chief advantage of the prior art excited frame vibratory conveyors.
While excited frame conveyors have worked with a great deal of success for a number of decades, several shortcomings have continued to present themselves during their use in various industries segments. Chief among these shortcomings relates to the difficulty in controlling the speed of product flow along the vibratory conveyor bed during operation. While it has long been known that the drive assemblies may be altered to provide different product flow characteristics, the adjustment from one flow characteristic to another often requires the addition or replacement of eccentric weights, or the substitution of new drives to achieve the change in the product speed. Further other difficulties with excited frame conveyors present themselves as the length of the conveyor bed, increases. Various schemes have been devised through the years for operating these longer length excited frame conveyors in a manner which avoids the problems associated with the excitation of frame structural frequency modes that may result in undesirable and even destructive motion of the conveyor bed or an entire conveyor system. A previous patent which addresses this problem is seen in U.S. Pat. No. 6,655,523, the teachings of which are incorporated by reference herein. Therefore, a vibratory conveyor which avoids the problems associated with the excited frame conveyors which are described in the prior art, and employed heretofore, is the subject matter of the present invention.